We propose to continue our studies on the chemical structure and mode of action of two new types of growth-regulating substances which are synthesized persistently by plant tumor cells and which are importantly involved in the establishment and maintenance of the tumorous state in cells of higher plant species. One of these is a potent cell division-promoting factor which has been assigned the trivial name cytokinesin I while the other is a cAMP(3'5')-like compound which appears to be the pyrophosphate derivative of authentic cAMP(3'5'). We also propose to continue our studies on the regulatory mechanisms involved in the persistent but reversible suppression of the tumorous state in plants. Our studies have suggested that positive feedback control mechanisms are involved in determining whether the normal phenotype or the tumor phenotype is expressed in transformed cells. We propose to study, at the biochemical level, how these positive feedback loops are established and maintained in cells that exhibit the tumor phenotype and how those loops are interrupted when the cells show the normal phenotype.